Electrical Resistance Calculator
Use this calculator to determine the electrical resistance of a circuit component using Ohm's Law, given the voltage across it and the current flowing through it.
Calculated Resistance:
Enter values and click 'Calculate'
Understanding Electrical Resistance
Electrical resistance is a fundamental property of a material that opposes the flow of electric current. Think of it as friction for electrons. The higher the resistance, the more difficult it is for current to pass through a material, and the more energy is dissipated, often as heat.
Ohm's Law: The Foundation
The relationship between voltage, current, and resistance is described by Ohm's Law, one of the most important principles in electronics. It states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them.
Mathematically, Ohm's Law is expressed as:
V = I × R
Where:
- V is the Voltage (measured in Volts, V) – the electrical potential difference that drives the current.
- I is the Current (measured in Amperes, A) – the rate of flow of electric charge.
- R is the Resistance (measured in Ohms, Ω) – the opposition to the flow of current.
Our calculator uses a rearranged version of this formula to find resistance:
R = V / I
Units of Measurement
- Volt (V): The unit of electrical potential difference or electromotive force. One volt is defined as the potential difference between two points that will impart one joule of energy per coulomb of charge passing through it.
- Ampere (A): The unit of electric current. One ampere is defined as one coulomb of charge passing a point in one second.
- Ohm (Ω): The unit of electrical resistance. One ohm is defined as the resistance between two points of a conductor when a constant potential difference of one volt, applied to these points, produces a current of one ampere.
How to Use the Resistance Calculator
- Enter Voltage: Input the voltage (in Volts) across the component or circuit you are analyzing into the "Voltage (Volts)" field.
- Enter Current: Input the current (in Amperes) flowing through that component or circuit into the "Current (Amperes)" field.
- Calculate: Click the "Calculate Resistance" button.
- View Result: The calculated resistance, in Ohms (Ω), will be displayed in the result area.
Practical Examples
Let's look at some real-world scenarios:
- Example 1: Simple LED Circuit
Suppose you have a 12V power supply and you want to power an LED that draws 20mA (0.02A) of current. To limit the current and protect the LED, you need a resistor.- Voltage (V) = 12 V
- Current (I) = 0.02 A
- Resistance (R) = V / I = 12 V / 0.02 A = 600 Ω
- Example 2: Heating Element
A heating element in a small appliance operates on a 240V supply and draws 10A of current. What is its resistance?- Voltage (V) = 240 V
- Current (I) = 10 A
- Resistance (R) = V / I = 240 V / 10 A = 24 Ω
- Example 3: Car Headlight
A car headlight bulb is designed for a 12V system and typically draws about 4.5A.- Voltage (V) = 12 V
- Current (I) = 4.5 A
- Resistance (R) = V / I = 12 V / 4.5 A ≈ 2.667 Ω
Factors Affecting Resistance (Beyond Ohm's Law)
While Ohm's Law defines the relationship between V, I, and R for a given circuit, the inherent resistance of a material itself is determined by several factors:
- Material: Different materials have different resistivities. Conductors (like copper) have low resistance, while insulators (like rubber) have very high resistance.
- Length: The longer the conductor, the greater its resistance.
- Cross-sectional Area: The wider the conductor, the lower its resistance (more space for electrons to flow).
- Temperature: For most conductors, resistance increases with temperature.
This calculator focuses on the practical application of Ohm's Law to find resistance in an active circuit, assuming the voltage and current are known.